In article ,
wrote:
A load that dropped the voltage by more than 10% would trip the breaker
first.
A demonstration of arrogance and stupicity in a single sentence -
quite typical for you.
NORMALLY a 15 amp outlet is wired with 14 guage copper, but many homes
built in the 60's and 70's used 12 guage aluminum wire. The
calculated voltage drop through a 100 ft run of 14 gauge copper NMC
cable carrying 15 amps would be 7.8 volts, aluminum would be 9.5
volts. HOWEVER, it is unlikely the wire runs directly from the
circuit breaker to the outlet in question, and we can't assume a
straight-line distance. Common wiring practice is to run the wire
back into the basement (or the attic) between outlets. If the attic,
each excursion would add 15 feet to the length. Also, each outlet
represents 2 (if using wire nuts) to 4 additional connections, each
increases the voltage drop slightly.
Also a factor: time. I've just looked at a couple of "current vs.
time-to-trip" curves for circuit breakers, and they seem to share some
common characteristics. Below a certain threshold (4x to 9x the
nominal rating), the breaker has a long (often *very* long) "time to
trip" - at 3x the nominal rating, the time-to-trip on these two is on
the order of 10 seconds. It isn't until you hit a higher-current
threshold that the breaker opens "instantaneously" (tens of
milliseconds or less).
Citations:
http://electrical-engineering-portal...current-curves
and Google on "circuit breaker trip curve" to find numerous other
example curves of the same general nature.
So, using the figures Bill cited above: if you drew 30 amps through a
100-foot 14-gauge aluminum-wire run, there would be 19 volts of
drop... and in the curves I'm seeing here, it looks as if the breaker
wouldn't open for over 20 seconds. That's more than a 10% drop in
nominal voltage, and this doesn't account for any voltage drop in the
outlet itself.
A current-draw surge of 45 amps would drop around 28 volts, and these
breakers wouldn't open for about 10 seconds (3x rated current draw).
This would put a nominal "120-volt" circuit down right around the
100-volt level.
I can tell you from personal experience, that if I start a 10"
hand-held circular saw (nominal draw about 6 amps I believe), and have
it plugged into a 15-amp circuit which shares an outlet with our den
and computer, the momentary surge of current draw when the motor
starts does *not* trip the breaker, but *does* cause the computer in
the den to abruptly power itself off - just as the original poster's
system did! I've had to learn not to use my power tools out by the
back shed (which has this shared circuit) when my wife is on-line...
the storm of "I lost the email I was writing" is just too painful to
bear :-)
--
Dave Platt AE6EO
Friends of Jade Warrior home page:
http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
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